This paper presents an ongoing research on developing an agent based system architecture for wireless sensor networks. The main objective of this system is to facilitate the design, implementation, and maintenance of applications for sensor networks that consist of wireless sensor nodes. The proposed system architecture contains four types of agents: interface, regional, cluster, and query agents. The interface agents receive queries from the users and return the results back to them. The regional agent is responsible for sending query packets to the cluster agents. The cluster agents disseminate query into the network and provide efficient in-network processing. Finally, the query agents process the query in the sensor node. The delegation of specific tasks to different software agents facilitates the development and maintenance of sensor network applications